Image-taking apparatus and system

ABSTRACT

There is disclosed an image-taking apparatus that prevents a defocus of a subject image observed after a viewfinder mode switches when the focus control uses the same focus detecting unit for OVF and EVF modes. The image-taking apparatus includes a focus detecting unit for detecting focus of the image-taking lens, and a mirror unit for switching between a first state used to introduce the light from the image lens into the viewfinder optical system and the focus detecting unit, and a second state used to introduce the light to the image-pickup device and the focus detecting unit. The controller controls driving of the mirror unit and driving of a focus lens based on a detection result by the focus detecting unit. The controller prohibits the driving of the mirror unit while the focus lens is being driven.

BACKGROUND OF THE INVENTION

The present invention relates to an image-taking apparatus, and moreparticularly to an image-taking apparatus that enables a user toarbitrarily switch a viewfinder mode by operating a mirror unit.

A single lens reflex camera as one image-taking apparatus reflects thelight emitted from an image-taking lens via a mirror closer to an imagesurface than the image-taking lens, and introduces the light to theoptical viewfinder (“OVF”). Thereby, a photographer can view an erectobject image formed by the image-taking lens. The mirror is obliquelyprovided on a shooting optical path.

In shooting an object image, the mirror retreats from the shootingoptical path, and enables the light from the image-taking lens to suchan imaging medium as a film and an image-pickup device, such as a CCD.After the shot, the mirror is obliquely arranged on the shooting opticalpath.

Some digital single lens reflex cameras can select two types offocusing, i.e., a manual phase difference detection and a contrastdetection (Japanese Patent Application, Publication No. 2001-275033).The phase difference detection determines focus when the mirror isobliquely provided on the shooting optical path, and the contrastdetection determines focus using an output from the image-pickup device,when the mirror retreats from the shooting optical path (Japanese PatentApplication, Publication No. 2001-125173). A camera of Japanese PatentApplication, Publication No. 2001-125173 electronically displays animage read from the image-pickup device on an electronic viewfinder(“EVF”), determines focus by the contrast detection, and measures thesubject brightness using an output from the image-pickup device.

In general, the contrast detection seeks a position having a maximum AFevaluation value by slightly moving the image-taking lens in the opticalaxis direction, and disadvantageously requiring a long time to determinefocus. On the other hand, the phase difference detection moves theimage-taking lens by a detected defocus amount, and needs a shorter timeto determine focus than the contrast detection.

Some digital single lens reflex cameras include a focus detecting unitof the phase difference detection in each of a lens unit and a camerabody (Japanese Patent Application, Publication No. 2000-162494).According to this camera, when a mirror used to switch an optical pathis located on the shooting optical path, the focus detecting unit in thecamera body detects focus, and when the mirror retreats from theshooting optical path, the focus detecting unit in the lens unit detectsfocus. Wherever the mirror moves, the focus detecting unit detects focusby the phase difference detection and accelerates focusing.

A camera that has the mode selector that selects a shooting modeactivates an EVF, when a mode selector selects a macro mode, andcaptures a subject image while enabling the subject image to be observedon the EVF. The camera deactivates the EVF in a shooting mode other thanthe macro mode, and captures a subject image while enabling the subjectimage to be observed on an OVF (Japanese Patent Application, PublicationNo. 10-336495).

Disadvantageously, the camera proposed in Japanese Patent Application,Publication No. 2000-162494 has the reduced imaging light intensity forthe camera body due to the mirror that introduces the light into thefocus detecting unit in the lens unit. In addition, since each of thelens unit and the camera body has the focus detecting unit, the lensunit becomes large and expensive.

The instant inventor has proposed a single lens reflex camera thatdisplaces a mirror unit on a shooting optical path and enables a user toarbitrarily switch between the OVF mode used to introduce the light fromthe image-taking lens to the viewfinder optical system and focusdetecting unit, and the EVF mode used to introduce the light into theimage-pickup device and the focus detecting unit (see the followingembodiment in this specification). This camera, whichever viewfindermode it has, detects focus by the focus detecting unit provided in thecamera body and control focus based on a detection result. This cameraretreats the mirror unit from the shooting optical path during theshooting time or image recording time.

In this camera, the EVF mode in which the light reaches the image-pickupdevice after transmitting through the mirror unit, offsets a focusposition of the subject image from a shooting time when the lightreaches the image-pickup device without intervening the mirror unit, bya change of the optical path length due to a refraction in the mirrorunit. Therefore, the EVF mode corrects a driving position of the focuslens, which is calculated based on the detection result by the focusdetecting unit, by the offset amount of the focus position. Thus, evenfor the same subject distance, the target driving position of the focuslens is different between focusing in the OFV mode and focusing in theEFV mode.

As a consequence, when the user switches a current viewfinder mode amongthe EVF and OFV modes to the other mode while the focus lens is beingdriven to the target position, a defocus occurs when the driving of thefocus lens ends due to the above difference between the target drivingpositions.

An application of a structure proposed in Japanese Patent Application,Publication No. 10-336495 to a single lens reflex camera causes a switchof viewfinder mode between the EVF and OVF modes when a shooting modeselector is operated in a playback mode use to play and display arecorded image. When the shooting mode is switched to the playback modeand the playback mode is switched back to the shooting mode, aphotographer feels discomfort because a viewfinder mode for the currentshooting mode is different from the viewfinder mode for the previousshooting mode.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an exemplary object of the present invention toprovide an image-taking apparatus that controls focus using the samefocus detecting unit for both the OFV and EVF modes, and prevents adefocus of a subject image observed after switching a viewfinder mode.Another illustrative object of the present invention is to provide animage-taking apparatus that eliminates a disadvantage associated with aswitch of the viewfinder mode from a playback mode to the shooting mode.

An image-taking apparatus according to one aspect of the presentinvention includes an image-pickup device for photoelectricallyconverting a subject image formed by light from an image-taking lens, aviewfinder optical system for enabling the subject image to be observedusing the light, a focus detecting unit for detecting focus of theimage-taking lens using the light, a mirror unit for switching between afirst state used to introduce the light into the viewfinder opticalsystem and the focus detecting unit, and a second state used tointroduce the light to the image-pickup device and the focus detectingunit, and a controller for controlling driving of the mirror unit anddriving of a focus lens in the image-taking lens based on a detectionresult by the focus detecting unit, wherein the controller prohibits thedriving of the mirror unit while the focus lens is being driven.

An image-taking apparatus according to another aspect of the presentinvention includes an image-pickup device for photoelectricallyconverting a subject image formed by light from an image-taking lens, aviewfinder optical system for enabling the subject image to be observedusing the light, a mirror unit for switching between a first state usedto reflect the light to the viewfinder optical system, and a secondstate used to transmit the light to the image-pickup device, and acontroller for controlling driving of the mirror unit, and for operatingbetween a first mode used to record an image using an output from theimage-pickup device, and a second mode used to display a playback image,wherein the controller prohibits the driving of the mirror unit whilethe focus lens is being driven.

Other objects and further features of the present invention will becomereadily apparent from the following description of the preferredembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a camera system at a second optical pathsplitting state according to one embodiment of the present invention.

FIG. 2 is a sectional view of the camera system according to thisembodiment, which is switching from a first optical path splitting stateto a second optical path splitting state.

FIG. 3 is a sectional view of the camera system of one embodiment in thefirst optical path splitting state.

FIG. 4 is a sectional view of the camera system of one embodiment, whichis switching from a first optical path splitting state to a thirdoptical path splitting state.

FIG. 5 is a sectional view of the camera system of one embodiment in thethird optical path splitting state.

FIG. 6 is a schematic view of an optical configuration of the camerasystem according to one embodiment.

FIG. 7 is a block diagram showing an electric configuration of thecamera system according to one embodiment.

FIG. 8 is a flowchart showing a viewfinder mode switching action in thecamera system according to one embodiment.

FIG. 9 is a flowchart of a shooting action of the camera systemaccording to a first embodiment.

FIG. 10 is a flowchart showing a switching action between a shootingmode and a playback mode in the camera system according to the firstembodiment.

FIG. 11 is a view showing an output signal waveform of a focus detectingsensor when the image-taking optical system is an out-of-focus state.

FIG. 12 is a view showing an output signal waveform of a focus detectingsensor when the image-taking optical system is an in-focus.

FIG. 13 is a view showing a relationship between an image pickup rangeand an image range which can be output to a display unit.

FIG. 14 is a view showing a relationship between an image pickup rangeand an image range which can be output to a display unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a description will be givenof the preferred embodiment.

FIGS. 1 to 7 show a camera (or shooting) system according to oneembodiment of the present invention. FIG. 6 shows a schematic opticalstructure of the camera system of this embodiment. This camera systemincludes a camera body (or an image-taking apparatus) and a lens unitthat is detachably attached to the camera body.

The camera is a one-CCD digital color camera that uses an image-pickupdevice, such as a CCD and a CMOS sensor, drives the image-pickup devicecontinuously or for each shot, and obtains an image signal indicative ofa motion or still image. The image-pickup device is an area sensor thatconverts the exposure light into an electric signal for each pixel, andstores and reads electric charges corresponding to the received lightintensity.

In FIG. 6, 100 denotes a camera body, and 101 denotes a lens unit thatis detachable from the camera body 100. The lens unit 101 includes astop 102 and an image-taking optical system 103. The lens unit 101 iselectrically and mechanically connected to the camera body 100 via aknown mounting mechanism. Shooting screens with various angles of fieldare available by connecting the lens units 101 having different focallengths to the camera body 100.

In focusing an image-taking optical system, the lens unit 101 moves afocus lens 103 b in an image-taking optical system 103 along an opticalaxis L1 via a driving mechanism (not shown), or makes the focus lens 103b of an flexible or elastic transparent element or liquid lens andvaries an interface shape and thus a refractive power.

106 denotes an image-pickup device housed in a package 124. On anoptical path from the image-taking optical system 103 to theimage-pickup device 106, an optical low-pass filter 156 is providedwhich restricts a cutoff frequency of the image-taking optical system103 and prevents excessively high space frequency component of theobject image (or optical image) from transmitting to the image-pickupdevice 106. The image-taking optical system 103 has an infrared ray (IR)cut filter (not shown).

A signal read from the image-pickup device 106 is displayed as imagedata on a display unit 107 after processed as follows. The display unit107 is attached to a back surface of the camera body 100, and a user candirectly observe a display on the display unit 107.

The display unit 107 that includes an organic EL spatial modulator, aliquid crystal spatial modulator, and a spatial modulator that utilizeselectrophoresis of fine particles saves the consumption power andbecomes thin, making the camera body 1 energy-efficient and small.

Specifically, the image-pickup device 106 is a CMOS process compatiblesensor (simply “CMOS sensor” hereinafter) as one amplification CCD. Onecharacteristic of the CMOS sensor is that a single process can form theMOS transistor and peripherals in the area sensor such as animage-pickup device driver, an AD converter and an image processor,remarkably reducing the number of masks and the processing step incomparison with the CCD. Another characteristic is a random access to anarbitrary pixel, which facilitates readout of a cut image for display,and provides real-time displays at a high display rate on the displayunit 107.

The image-pickup device 106 uses the above characteristics to outputimages to be displayed (partially cut readouts of the light receivingarea on the image-pickup device 106) and to output fine images (fullreadouts of the light receiving area).

111 denotes a movable half mirror (a first mirror member) for reflectingpart of the light from the image-taking optical system 103, and fortransmitting the rest of the light. The half mirror 111 has a refractiveindex of about 1.5 and a thickness of 0.5 mm. 105 denotes a focusingscreen arranged on an expected imaging surface of the object imageformed by the image-taking optical system 103. 112 denotes a pentaprism.

109 denotes a viewfinder lens that observes an object image formed onthe focusing screen, and actually includes three viewfinder lenses109-1, 109-2 and 109-3 in FIG. 1. The focusing screen 105, thepentaprism 112 and the viewfinder lens 109 constitute a viewfinderoptical system.

A movable sub-mirror (or a second mirror member) 122 is provided behindthe half mirror 111 (at the image surface side), which reflects andintroduces to the focus detecting unit 121 the light that hastransmitted through the half mirror 111 and close to the optical axisL1. The sub-mirror 122 rotates around a rotating axis 125 (see FIG. 1etc.), which will be described later, and is housed in the lower portionof the mirror box in accordance with an action of the half mirror 111.The sub-mirror 122 is not operably integrated with the half mirror, andindependently projects to and retreats from the shooting optical path.

The focus detecting unit 121 receives the light from the sub-mirror 122,and determines focus by the phase difference detection.

An optical path splitting system that includes the half mirror 111 andthe sub-mirror 122 is adapted to switch among first to third opticalpath splitting states, as described later. In the first optical pathsplitting state (or a first state), the light from the image-takingoptical system 103 is reflected on the half mirror 111 and introduced tothe finder optical system, while the light that has transmitted throughthe half mirror 111 is reflected on the sub-mirror 122 and introduced tothe focus detecting unit 121.

The first optical path splitting state enables the object image formedby the above light to be observed via the viewfinder lens 109, and thefocus detecting unit 121 to detect focus. FIG. 6 shows the first opticalpath splitting state.

In the second optical path splitting state, the light from theimage-taking optical system 103 transmits through the half mirror 111,reaches the image-pickup device 106 through the half mirror 111, and isreflected on the half mirror 111 and introduced to the focus detectingunit 121. The second optical path splitting state enables the capturedimage data to be displayed on the real-time basis on the display unit107, and provides high-speed continuous shooting. Since the secondoptical path splitting state does not drive the optical path splittingsystem in shooting by the image-pickup device 106, the high-speedcontinuous shooting is available by accelerating operations in thesignal processing system.

The second optical path splitting state enables the focus detecting unit121 to determine focus. Therefore, during monitoring on the display unit107, the high-speed focusing is available by the phase differencedetection.

Since the light from the image-taking optical system 103 reaches theimage-pickup device 106 in the second optical path splitting state, thecontrast detection that uses an output from the image-pickup device 106may determine focus, in addition to the above focusing by the phasedifference detection, for more highly precise focusing.

The third optical path splitting state directly introduces the lightfrom the image-taking optical system 103 to the image-pickup device 106,and retreats the half mirror 111 and sub-mirror 122 from the shootingoptical path. The third optical path splitting state is used to generatea fine image suitable for large printing etc.

A mirror driving mechanism having an electromagnetic motor and gears(not shown) switches the optical path splitting system among the firstto third optical path splitting states by displacing the half mirror 111and the sub-mirror 122, respectively. A camera system controller 135controls driving of the mirror driving mechanism via a mirror drivingcontroller 145 as described later.

The half mirror 111 is made of lightweight transparent resin for quicklyswitching among the above three optical path splitting states. Abirefringent polymer thin coating is pasted on the back surface of thehalf mirror 111 (or a surface on the side of sub-mirror 122 in FIG. 6).This provides a strong low-pass effect when the shot does not use allthe pixels of the image-pickup device 106, for example, for imagemonitoring (with a real-time display) and high-speed continuousshooting.

A fine pyramid periodic structure having a pitch smaller than awavelength of the visible light on the surface of the half mirror 111may provide a so-called photonic crystal effect to reduce the surfacereflection caused by the refractive index difference between the air andresin and to improve light use efficiency. This structure prevents theghost due to multi-reflections on the front and back surfaces of thehalf mirror 111.

104 denotes a movable flashing unit that is movable between anaccommodated position at which the unit is housed in the camera body 100and an emission position at which the unit projects from the camera body100. 113 denotes a focal plane shutter that adjusts the light intensityincident upon the image surface. 119 denotes a main switch thatactivates the camera body 100.

120 denotes a two-stage pressing release button. The half-press (SW1 ON)starts a shooting preparation, such as photometry and focusing, and thefull-press (SW2 ON) starts shooting (or storing image data read from theimage-pickup device 106 in the recording medium).

123 denotes a viewfinder mode switch that switches between the OVF andEVF modes whenever it is pressed. 127 denotes a shooting/playback modeswitch as an operation member, which switches between a playback mode asa second mode used to play and display shot images, and a shooting modeas a first mode relating to shooting including a viewfinder observationand recording of an image.

180 denotes an information display unit in the OVF, and displaysspecific information on the focusing screen 105.

FIG. 7 is a block diagram showing an electric configuration of a camerasystem in this embodiment. Here, those elements described with referenceto FIG. 6 are designated by the same reference numerals. A descriptionstarts with the shooting and recording of an object image.

The camera system includes an image-taking system, an image processingsystem, a recording/playback system, and a control system. Theimage-taking system includes the image pickup optical system 103 andimage-pickup device 106. The image processing system includes an A/Dconverter 130, a RGB image processor 131, and a YC image processor 132.The recording/playback system includes a recording processor 133 and aplayback processor 134. The control system includes a camera systemcontroller 135 that serves as a controller of the camera system, anoperation detecting circuit 136, and an image-pickup device driver 137.

138 denotes a standardized connection terminal connectable to anexternal computer etc. for data communications. The above electriccircuit drives in response to power supply from a small fuel battery(not shown).

The image-taking system is an optical processing system that images thelight from the object onto the image pickup surface of the image-pickupdevice 106 via the image pickup optical system 103. Control over ashutter (not shown) in the image pickup optical system 103 and necessarydriving of the focal plane shutter 113 will allow the image-pickupdevice 106 to receive the object light at proper light intensity.

The image-pickup device 106 uses an image-pickup device having totallyabout 10 million pixels with 3,700 square pixels in a longitudinaldirection and 2,800 square pixels in a lateral direction. R (red), G(green) and B (blue) color filters are alternately arranged onrespective pixels to form a so-called Bayer arrangement having pluralsets of four pixels.

The Bayer arrangement improves collective image performance by arrangingmore G pixels which an observer feels more strongly in viewing an imagethan R and B pixels. In general, image processing using this type ofimage-pickup device generates a brightness signal mainly from G and acolor signal from RGB.

A signal read from the image-pickup device 106 is supplied to an imageprocessing system via the A/D converter 130, and the image processingsystem generates image data through image processing.

The A/D converter 130 is a signal converter that converts, in accordancewith the amplitude of a signal read from each pixel of the image-pickupdevice 106, an output signal from the image-pickup device 106 into, forexample, a 10-bit digital signal and outputs the signal. As a result,the subsequent image processing is executed digitally.

The image processing system is a signal processor to obtain an imagesignal of a desired format from the RGB digital signals, and convertsthe RGB color signals into a YC signal that is expressed by a brightnesssignal Y and a color-difference signal (R-Y) and (B-Y), or anothersignal.

The RGB image processor 131 is a signal processor that processes anoutput signal from the A/D converter 130, and includes a white balancecircuit, a y-correction circuit, and an interpolation operator thatprovide high resolution using the interpolation operation.

The YC processor 132 is a signal processor that generates the brightnesssignal Y and color-difference signals R-Y and B-Y. This YC processor 132includes a high-range brightness signal generator for a high-rangebrightness signal YH, a low-range brightness signal for a low-rangebrightness signal YL, and a color-difference generator that generatesthe color-difference signals R-Y and B-Y. The brightness signal Y isformed by synthesizing the high-range and low-range brightness signalsYH and YL.

The recording/playback system is a processing system that outputs animage signal to a memory (not shown) and an image signal to the displayunit 107. The recording processor 133 writes down the image signal inand reads out the image signal from the memory, and the playbackprocessor 134 reproduces the image signal read from the memory, andoutputs it to the display unit 107.

The recording processor 133 includes a compression/decompression circuitthat compresses the YC signal indicative of the still and motion-pictureimage data in a predetermined compression format, and decompresses thecompressed data. The compression/decompression circuit includes a framememory etc. for signal processing, and stores the YC signal from theimage processing system in this frame memory, reads, compresses andencodes a stored signal from each of plural blocks. The compression andencoding may, for example, use a two-dimensional orthogonal conversion,normalization and Huffman coding of the image signal for each block.

The playback processor 134 is a circuit that matrix-converts thebrightness signal Y and color-difference signals R-Y and B-Y, forexample, into the RGB signal. A signal converted by the playbackprocessor 134 is output to the display unit 107, and displayed orreproduced as a visual image. The playback processor 134 and the displayunit 107 may be connected via a wireless communication means, such asBluetooth, and this configuration enables the image shot by this camerato be monitored at a remote location.

The operation detecting circuit 136 in the control system detectsoperations of a main switch 119, a release button 120, and a viewfinderswitch 123, a shooting/playback switch 127, and other switches (althoughthe other switches are not shown), and outputs the detection result tothe camera system controller 135.

The camera system controller 135 receives the detection signal from theoperation detecting circuit 136, and operates in accordance with thedetection result. The camera system controller 135 generates a timingsignal for shooting and outputs it to the image-pickup device driver137.

The image-pickup device driver 137 generates a driving signal used todrive the image-pickup device 106 in response to a control signal fromthe camera system controller 135. The information display circuit 142receives a control signal from the camera system controller 135, andcontrols driving of the OVF information display unit 180.

The control system controls driving of the image-taking system, imageprocessing system and recording/playback system in response tooperations of various switches of the camera body 100. For example, whena press of the release button 120 turns on SW2, the control system (orthe camera system controller 135) controls driving of the image-pickupdevice 106, operations of the RGB image processor 131, and compressionof the recording processor 133. In addition, the control system controlsdriving of the OVF information display unit 180 via the informationdisplay circuit 142, and changes a display (or a state of the displayedsegment) in the OVF.

The mirror driving controller 145 receives a control signal from thecamera system controller 135, and controls driving of the mirror motor146 as a driving source of the half mirror 111 and the sub-mirror 122(which are not shown in FIG. 7). The driving force of the mirror motor146 is transmitted to a mirror driving mechanism 150, and the halfmirror 111 and sub-mirror 122 can switch among the first to thirdoptical path splitting states as described above.

A description will now be given of focusing of the image pickup opticalsystem 103.

The camera system controller 135 is connected to an AF controller 140.The camera system controller 135 is connected to a lens systemcontroller 141 in the lens unit 101 via mount contacts 100 a and 101 awhen the lens unit 101 is attached to the camera body 100. The camerasystem controller 135 transmits necessary for specific processing to andreceives the data from AF controller 140 and the lens system controller141.

The focus detecting unit 121 (or focus detecting sensor 167) outputs tothe AF controller 140 a detection signal from a focus detection areathat is provided in place on a shooting screen. The AF controller 140generates a focus detecting signal based on an output signal from thefocus detecting unit 121, and detects a focus state (or a defocusamount) of the image pickup optical system 103. The AF controller 140converts the detected defocus amount into a driving amount of the focuslens 103 b, and sends the information on the driving amount of the focuslens 103 b to the lens system controller 141 via the camera systemcontroller 135.

In focusing the moving object, the AF controller 140 predicts a properstop position of the focus lens 103 b by considering the time lag fromthe full press of the release button 120 to an actual start of the imagepickup control. The information on the driving amount of the focus lens103 b to the predicted stop position is sent to the lens systemcontroller 141.

When the camera system controller 135 determines that the brightness ofthe object is too low to obtain the sufficient focus detecting accuracybased on the output signal of the image-pickup device 106, the flashingunit 104 or the white LED or fluorescent tube (not shown) of the camerabody 100 is driven to illuminate the object.

When the lens system controller 141 receives the information on thedriving amount of the focus lens from the camera system controller 135,the lens system controller 141 controls driving of the AF motor 147 inthe lens unit 101 and moves the focus lens 103 b along the optical axisL1 by the driving amount via the driving mechanism (not shown). Thereby,the image pickup optical system 103 is at the in-focus state. Asdescribed above, if the focus lens includes a liquid lens etc., theinterface shape will be changed.

When the lens system controller 141 receives information on an exposure(or stop) value from the camera system controller 135, the lens systemcontroller 141 controls driving of the stop driving actuator 143 in thelens unit 101 and operates the stop 102 so that it has an aperturediameter corresponding to the above aperture value, thereby directingthe object light at the proper light intensity to the image surfaceside.

When the AF controller 140 detects focus on the object, the detectionresult is sent to the camera system controller 135. When the full pressof the release button 120 turns on SW2, the shooting follows through theimage-taking system, image processing system and recording/playbacksystem as described above.

FIGS. 1 to 5 are sectional views of the camera system of thisembodiment, and show part of the lens unit 101. Those elements describedwith reference to FIG. 6 are designated by the same reference numerals.

FIG. 1 is a sectional view of the camera system in the second opticalpath splitting state. FIG. 2 is a sectional view of the camera systemthat is switching from the first optical path splitting state to thesecond optical path splitting state. FIG. 3 is a sectional view of thecamera system in the first optical path splitting state. FIG. 4 is asectional view of the camera system that is switching from the firstoptical path splitting state to the third optical path splitting state.FIG. 5 is a sectional view of the camera system in the third opticalpath splitting state.

Referring now to FIG. 3, a description will be given of theconfiguration of the camera system when the optical path splittingsystem as the mirror unit that includes the half mirror 111 andsub-mirror 122 is in the above first optical path splitting state.

In FIG. 3, 100 denotes a camera body, and 101 denotes a lens unit. Thelens unit 101 is attached to a camera mount 100 b via a lens mount 101b. 103 a denotes an image-taking lens closest to the image surface amongplural lenses in the image pickup optical system 103. 105 denotes afocusing screen in the viewfinder optical system. 107 denotes a displayunit. 163 denotes an eyepiece shutter.

164 denotes a condenser lens as a light receiving window in the focusdetecting unit 121. 165 denotes a mirror that reflects the light fromthe condenser lens 164. 166 denotes a re-imaging lens for imaging thelight reflected on the mirror 165 onto the focus detecting sensor 122.122 denotes a focus detecting sensor.

111 denotes a movable half mirror that is held on a half-mirrorreceiving plate (not shown). Pins 173 are provided at both side edges ofthe half-mirror receiving plate in the direction perpendicular to thepaper. A pin 174 is provided at one side edge in the directionperpendicular to the paper. The half mirror 111 and pins 173 and 174move together.

170 denotes a half-mirror driving lever, and 171 denotes a half-mirrorsupport arm. The half-mirror driving lever 170 is rotatably supportedaround a rotating shaft 170 a that is fixed on the camera body 100, andthe half-mirror support arm 171 is rotatably supported around therotating shaft 171 a that is fixed on the camera body 100.

The half-mirror support arm 171 is connected to an approximatelysimilarly shaped structure provided at the wall surface side opposing tothe mirror box via a connector 171 b. The pins 173 at both sides of thehalf-mirror receiving plate (not shown) are engaged with the perforationholes 171 c at the top of the half-mirror support arm 171. Thereby, thehalf mirror 111 is rotatable around the perforation hole 171 c via thehalf-mirror receiving plate.

The half-mirror receiving plate is forced in the arrow A direction by atorsion spring (not shown) that is located in the middle of the pins 173and 174, and the force of the torsion spring is also applied to the halfmirror 111 via the half-mirror receiving plate.

In the first optical path splitting state, the mirror stoppers 160 and161 project into the moving area of the half mirror 111, and contact thehalf mirror due to the force by the torsion spring. There are slightapertures between the pin 173 and a first cam surface 170 b of thehalf-mirror driving lever 170, and between the pin 174 and a second camsurface 170 b of the half-mirror driving lever 170. Thereby, the halfmirror 111 is positioned as shown in FIG. 3.

The mirror stoppers 160 and 161 can project into and retreat from themoving area of the half mirror 111 due to driving of the mirror drivingmechanism 150. The mirror stoppers 160 and 161 are located outside theshooting optical path in place that does not affect the shooting light,irrespective of whether or not they are located in the moving area ofthe half mirror 111. The following mirror stoppers 175 and 176 aresimilarly located outside the shooting optical path.

The sub-mirror 122 is rotatable around the rotating shaft 125, and heldat a position that reflects the transmission light from the half mirror111 to the side of the focus detecting unit 121 or the condenser lens164 as shown in FIG. 3 in the first optical path splitting state.

In the first optical path splitting state, part of the light from theimage pickup optical system 103 is reflected on the half mirror 111 andintroduced into the viewfinder optical system, and the rest of the lighttransmits through the half mirror 111, is reflected on the sub-mirror122, and is introduced into the focus detecting unit 121.

When the mirror stoppers 160 and 161 shown in FIG. 3 retreat from themoving area of the half mirror 111, the half mirror 111 shifts to thestate shown in FIG. 2 due to the force in the arrow A direction by thetorsion spring (not shown). Due to the force by the torsion spring, thepin 173 contacts the first cam surface 170 b of the half-mirror drivinglever 170 and the pin 174 contacts the second cam surface 170 c of thehalf-mirror driving lever 170.

The pins 173 and 174 slide along the first and second cam surfaces 170 band 170 c as the half-mirror driving lever 170 rotates, and theorientation of the half mirror 111 changes: The half-mirror support arm171 rotates as the the half-mirror driving lever 170 rotates, and thehalf-mirror receiving plate (not shown) and the half mirror 111 movetogether, which half-mirror receiving plate is connected to thehalf-mirror driving lever 170 and the half-mirror support arm 171 viathe pins 173 and 174.

As the half-mirror driving lever 170 and the half-mirror support arm 171rotate counterclockwise in FIG. 3, the half mirror 111 contacts themirror stoppers 175 and 176 as shown in FIG. 1. Since the half mirror111 receives the force in the arrow A direction from the torsion spring(not shown), it is held at the state shown in FIG. 1 or in the secondoptical path splitting state.

In shifting the half mirror 111 from the first optical path splittingstate to the second optical path splitting state, the sub-mirror 122rotates around the rotating shaft 125 clockwise in FIG. 3 and moves tothe lower part of the mirror box: Before the half mirror 111 shifts fromthe first optical path splitting state to the second optical pathsplitting state, the sub-mirror 122 moves to the lower part of themirror box, preventing the collision between the half mirror 111 and thesub-mirror 122.

In the second optical path splitting state, part of the light from theimage-taking lens 103 a is reflected on the half mirror 111 andintroduced to the focus detecting unit 121 as shown in FIG. 1, and therest of the light transmits the half mirror 111 and reaches theimage-pickup device 106.

In shifting the first optical path splitting state (FIG. 3) to the thirdoptical path splitting state (FIG. 5), the half-mirror driving lever 170rotates clockwise in FIG. 3 and retreats the half mirror 111 from theshooting optical path to the upper part in the camera body 100 (towardsthe focusing screen 105). As the sub-mirror 122 rotates around therotating shaft 125 clockwise in FIG. 3, the sub-mirror 122 retreats fromthe shooting optical path to the lower portion in the camera body 100.

In the third optical path splitting state, the light from theimage-taking lens 103 a reaches the image-pickup device 106 as shown inFIG. 5.

A description will now be given of the viewfinder mode switching actionin the above structured camera system.

While the electric circuits act in the camera system, the camera systemcontroller 135 monitors states of various switches in the camera body100 via the operation detecting circuit 136. The camera systemcontroller 135 starts switching the viewfinder mode as soon as itdetects the operation of the viewfinder mode switch 123 (step S120 inFIG. 9).

FIG. 8 is a flowchart for explaining the viewfinder mode switchingaction.

In step S200, the camera system controller 135 detects a currentviewfinder mode, and the flow proceeds to step S201 when the operationof the viewfinder mode switch 123 commands switching from the OVF modeto the EVF mode. On the other hand, when a switch from the EVF mode tothe OVF mode is directed, the flow proceeds to step S211.

A description will now be given of a switch from the OVF mode to the EVFmode. In the OVF mode, the half mirror 111 and the sub-mirror 122 are inthe first optical path splitting state (FIG. 3). Since the EVF mode doesnot introduce the object light to the viewfinder optical system, theeyepiece shutter 163 closes in the step S201: The camera system 135controls driving of the eyepiece shutter driver (not shown), and movesthe eyepiece shutter 163 to the optical path in the viewfinder opticalsystem.

This attempts to prevent a user from considering it a breakdown bymistake that he cannot view the object image via the viewfinder opticalsystem, and to prevent the light outside the camera from entering thecamera body 100 and finally the image-pickup device 106 via the eyepiecepart of the viewfinder optical system and from causing the ghost.

Step S202 deactivates the viewfinder field in the OVF informationdisplay unit 180 through control over driving of the information displaycircuit 142.

Since the eyepiece shutter 163 has closed through step S201, the userviews nothing even when he attempts to display specific information inthe finder field. This configuration stops driving the OVF informationdisplay unit 180 and restrains unnecessary power and batteryconsumptions in the camera system.

Step S203 moves the sub-mirror 122 to the lower part of the mirror boxand retreats it from the shooting optical path so as to transfer thehalf mirror 111 to the second optical path splitting state.

Step S204 controls driving of the mirror driving controller 145 andretreats the mirror stoppers 160 and 161 from the moving area of thehalf mirror 111. After the mirror stopper 160 and 161 retreat, the stepS205 rotates the half-mirror driving lever 170 counterclockwise in FIG.3 and the half mirror 111 transfers to the second optical path splittingstate (FIG. 1) via the state shown in FIG. 2 due to the (arrow A) forceof the spring (not shown).

As a result, part of the light emitted from the image-taking lens 103 ais reflected on the half mirror 111 and introduced into the focusdetecting unit 121, and the rest of the light transmits the half mirror111 towards the image surface side.

In the second optical path splitting state (FIG. 1), there are slightapertures between the pin 173 and the first cam surface 170 b of thehalf-mirror driving lever 170 and the pin 174 and the second cam surface170 c of the half-mirror driving lever 170. The half mirror 111 contactsthe mirror stoppers 175 and 176 and is thereby positioned.

A position of the reflection surface of the half mirror 111 in thesecond optical path splitting state is approximately equal to theposition of the sub-mirror 122 in the first optical path splittingstate. This configuration can prevent a positional offset of the lightincident upon the focus detecting unit 121 between the first and secondoptical path splitting states.

In the second optical path splitting state, the light from theimage-taking lens 103 a transmits through and refracts in the halfmirror 111, and then reaches the image-pickup device 106. A focusposition of the object image on the image-pickup device 106 formed bythe light that has transmitted through the half mirror 111 slightlyoffsets from the position on the image-pickup device 106 to which thelight reaches without transmitting the half mirror 111.

Therefore, step S206 runs a focus correction mode and corrects the aboveoffset of the focus position.

In this embodiment, a focus detecting signal output from the focusdetecting unit 121 in the first optical path splitting state indicates afocus position when the light from the image-taking lens 103 a directlyreaches the image-pickup device 106 in the third optical path splittingstate. On the other hand, when the focus correction mode is set in thesecond optical path splitting state, the above focus detecting signal iscorrected so as to indicate focus of the light from the image-takinglens 103 a which transmits through the half mirror 111 and reaches theimage-pickup device 106. Therefore, the focus position of the focus lens103 b in the image-taking optical system 103 in the second optical pathsplitting state offsets by a correction amount of the focus detectingsignal from the focus position in the first and third optical pathsplitting states.

Therefore, in shooting by turning on SW2 in the EVF mode, or inswitching the optical path splitting system from the second optical pathsplitting state to the third optical path splitting state, a frontcurtain driving mechanism of the focal plane shutter 113 is charged andthe position of the focus lens 103 b is corrected by the above offsetamount: The focus lens 103 b moves from the focus position in the secondoptical path splitting state to the focus position of the third opticalpath splitting state. Then, the focal plane shutter 113 opens for apredetermined time period for shooting by the image-pickup device 106.

The above configuration enables a focused image to be confirmed on thedisplay unit 107 in the EVF mode (or in the second optical pathsplitting state), and a focused image to be captured even in shooting inthe third optical path splitting state.

Step S207 precedes the front curtain of the focal plane shutter 113 forthe bulb exposure, allowing the object light that has transmitted theimage-taking optical system 103 to continuously reach the image-pickupdevice 106 and the image to be displayed on the display unit 107.

Step S208 powers on the display unit 107. Step S209 continues theimage-pickup device 106's image pickup action of the object image thatis formed by the image-taking optical system 103, and allows the imagedata read from the image-pickup device 106 and processed, to bedisplayed on the display unit 107 on a real-time basis. This is an endof a switching action from the OVF mode to the EVF mode.

In the second optical path splitting state or the EVF mode, the lightfrom the image-taking lens 103 a refracts in the half mirror 111 andreaches the image-pickup device 106. Therefore, as shown in FIG. 13, thelight receiving area 190 of the image-pickup device 106 in the secondoptical path splitting state may slightly offset from the lightreceiving area of the image-pickup device 106 in the third optical pathsplitting state in the longitudinal direction of the image-pickup device106 in FIG. 1. In other words, the real-time displayed image on thedisplay unit in the second optical path splitting state may not accordwith the image captured in the third optical path splitting state.

An area 190 a that does not overlap an area 191 in the area 190 isdisplayed on a real-time basis on the display unit 107, but is notincluded in an area shot in the third optical path splitting state.

The camera of this embodiment blacks out the area 192 corresponding tothe area 190 a in the image area displayed on the display unit 107 on areal-time basis (FIG. 13) as shown in FIG. 14, and prevents a display ofthe entire area 190. The playback processor 134 handles this process.

This configuration prevents a problem in that actually shot imagesinclude an image that is not displayed on the display unit 107 on areal-time basis.

A description will now be given of a transfer from step S200 to stepS211 to switch the EVF mode to the OVF mode.

In the EVF mode, the half mirror 111 and the sub-mirror 122 are in thesecond optical path splitting state (FIG. 1), and the display unit 107provides a real-time display.

Steps S211 stops driving of the display unit 107 and image pickup actionby the image-pickup device 106.

Step S212 runs a back curtain of the focal plane shutter 113, thuscloses the shutter, and charges the front and back curtain drivingmechanisms for a shooting preparation. Step S213 retreats the mirrorstoppers 160 and 161 from the moving area of the half mirror 111 andallows a movement of the half mirror 111 in the subsequent steps.

Step S214 rotates the half-mirror driving lever 170 clockwise in FIG. 1and transfers only the half mirror 111 in order of the state shown inFIG. 2, the state shown in FIG. 3, the state shown in FIG. 4, and thestate shown in FIG. 5. The half mirror 111 shifts to the third opticalpath splitting state (FIG. 5) via the first optical path splitting state(FIG. 3).

Step S215 moves the mirror stoppers 160 and 161 in the moving area ofthe half mirror 111, and moves the half mirror 111 to a predeterminedlocation for positioning.

As described above, the half mirror 111 is shifted to the third opticalpath splitting state after the mirror stoppers 160 and 161 are retreatedfrom the moving area of the half mirror 111, and then the mirrorstoppers 160 and 161 are moved in the moving area of the half mirror111. Therefore, the half mirror 111 does not collide with the mirrorstopper 160 and 161, and the mechanical reliability improves inswitching the OFV mode to the EVF mode.

Step S216 rotates the half-mirror driving lever 170 counterclockwise inFIG. 5, and turns the half mirror 111 from the third optical pathsplitting state (FIG. 5) to the first optical path splitting state (FIG.3) via the state shown in FIG. 4. Here, the half mirror 111 receives theforce of a spring (not shown) in the mirror driving mechanism 150, andcontacts the mirror stoppers 160 and 161.

Step S217 opens the eyepiece shutter 163 in the viewfinder opticalsystem.

In step S218, the camera system controller 135 determines whether or nota manual focus mode is set, based on an operation status of an AF/MFswitch (not shown) in the camera system. When the manual focus mode isset, the flow proceeds to step S208. When the manual focus mode is notset and the autofocus mode is set, the flow proceeds to step S220.

In the manual focus mode, it is unnecessary to operate the focusdetecting unit 121, and use of the EVF instead of the OVF provides adefocus amount of the background (subject image) more precisely.Therefore, when the manual focus mode is set, the flow proceeds to stepS204 for the real-time display on the display unit 107. When the flowproceeds from the step S218 to S204, the eyepiece shutter 163 is closed.

Step S220 moves the sub-mirror 122 into the shooting optical path at apredetermined position to introduce to the focus detecting unit 121 theobject light that has transmitted through the half mirror 111. Duringthe processes from step S211 to S218, the sub-mirror 122 is located at aposition of the second optical path splitting state (FIG. 1) or aposition that retreats from the shooting optical path, and operates whenthe flow proceeds to step S220.

In step S221, the camera system controller 135 drives the OVFinformation display unit 180, and activates the information displayfunction in the viewfinder. This is an end of a switch from the EVF modeto the OVF mode.

This embodiment sets the second optical path splitting state (FIG. 1) tothe optical path splitting system that includes the half mirror 111 andthe sub-mirror 122 in displaying a shot image on the display unit 107 orin the EVF mode, and introduces the light from the image-taking lens 103a to the focus detecting unit 121. This accelerates focusing in the EVFmode by the phase difference detection at the focus detecting unit 121.

Referring now to FIG. 9, a description will be given of the shooting inthe camera system of this embodiment. In shooting, the display unit 107provides the real-time display in accordance with a setting of theviewfinder mode, and the viewfinder field displays specific informationdue to driving of the OVF information display unit 180.

Step S100 sets the input ready state from a switch, such as the releasebutton 120. In step S101, the camera system controller 135 determineswhether or not there is any inputs from various switches in the camerabody 100 via the operation detecting circuit. When there is an inputfrom the switch, the flow proceeds to step S102.

Step S102 determines whether or not an input signal detected in stepS101 is an input of SW1 by the half-press of the release button 120.When it is the SW1 input, the flow proceeds to step S103; when not, theflow proceeds to step S120.

In step S120, the camera system controller 135 operates in accordancewith the input signal. For instance, it switches the viewfinder mode, orsends information on a aperture value to the lens system controller 141when the user sets the aperture value. The lens system controller 141that receives the information on the aperture value operates the stop102 by controlling driving of the stop driving actuator 143.

In step S103, the camera system controller 135 calculates the subjectbrightness based on an output from a photometric sensor (not shown) inthe camera body 100 (photometry). The AF controller 140 detects focus(or a defocus amount) of the image-taking optical system 103 based on anoutput of the focus detecting sensor 167 (focus detection).

Step S104 drives the focus lens 103 b based on a driving amount of thefocus lens 103 b obtained from the focus detection result (or a defocusamount) in step S103. More specifically, the camera system controller135 sends to the lens system controller 141 information on driving(amount and direction) of the focus lens 103 b obtained from the defocusamount. The lens system controller 141 moves the focus lens 103 b alongthe optical axis L1 by driving the AF motor 147.

Step S105 prohibits or invalidates an input of the viewfinder modeswitch 123 approximately simultaneous with a driving start of the AFmotor 147, and the flow proceeds to step S106.

The following problem occurs when the viewfinder mode switches inaccordance with the input of the viewfinder mode switch 123 while thefocus lens 103 b is being driven:

As discussed above, when the focus correction mode turns on in the EVFmode, the output signal of the focus detecting unit 121 is corrected andan offset occurs between a focus position of the focus lens 103 b in theEVF mode and a focus position of the focus lens 103 b in the OVF mode.Therefore, when driving of the focus lens 103 b starts at one viewfindermode among the OVF and EVF modes, and the viewfinder mode switchesduring this driving, the object image observed in the switchedviewfinder mode defocuses after the driving of the focus lens 103 bends.

Accordingly, this embodiment invalidates the input of the viewfindermode switch 123 during the driving of the focus lens 103 b, preventingswitching of the viewfinder mode and the above defocus of the objectimage.

In step S106, the camera system controller 135 determines whether or notthere is an input of SW2 via the operation detecting circuit 136. Whenthere is no SW2 input, the flow proceeds to step S130, whereas whenthere is a SW2 input, the flow proceeds to step S107.

In step S130, the lens system controller 141 sends a focus completionsignal to the camera system controller 135 after finishing driving ofthe AF motor 147 or moving the focus lens 103 b to a predeterminedin-focus position. The camera system controller 135 determines whetheror not driving of the AF motor 147 ends based on a communication withthe lens system controller 141. When the driving of the AF motor 147 hasnot yet been completed, the flow proceeds to step S106, and when thedriving of the AF motor is completed, the flow proceeds to step S131.

Step S131 validates an input of the viewfinder mode switch 123, whichwas prohibited by the step S105, and the flow returns to step S102.

Step S107 turns the optical path splitting system to the third opticalpath splitting state (FIG. 5) by controlling driving of the mirrordriving controller 145. More specifically, in shooting in the EVF mode,the half mirror 111 in the second optical path splitting state isretreated from the shooting optical path and turned to the third opticalpath splitting state. In shooting in the OVF mode, the half mirror 111and the sub-mirror 122 in the first optical path splitting state areretreated from the shooting optical path and turned to the third opticalpath splitting state.

In step S108, the camera system controller 135 sends to the lens systemcontroller 141 information on a aperture value obtained by thephotometric action of the step S103. The lens system controller 141 thathas received the information on the aperture value operates the stop 102in accordance with the aperture value by controlling driving of the stopdriving actuator 143.

When it is determined that the driving of stop 102 is unnecessary basedon the photometric result of step S103, the flow proceeds to step S109with no process of step S108.

In step S109, the camera system controller 135 starts exposing theimage-pickup device 106 after opening the focal plane shutter 113. Thisstarts shooting, and the signal read from the image-pickup device 106 isproperly processed through the RGB image processor 131, the YC processor132 and the recording processor 133. The processed image data isrecorded in a recording medium (not shown) and displayed on the displayunit 107 via the playback processor 134.

Step S110 validates an input of the viewfinder mode switch 123, whichwas prohibited by step S105, and proceeds to step S111. The process ofstep S110 may be the same as that of step S109.

In step S111, the camera system 135 controls driving of the mirrordriving controller 145, and turns the third optical path splitting stateto the first or second optical path splitting state: In the EVF mode,the half mirror 111 in the third optical path splitting state isadvanced into the shooting optical path and turned to the second opticalpath splitting state. In the OVF mode, the half mirror 111 and thesub-mirror 122 in the third optical path splitting state are advancedinto the shooting optical path and turned to the first optical pathsplitting state.

Referring now to FIG. 10, a description will be given of switchingbetween the shooting mode and the playback mode by the shooting/playbackmode switch 127.

The camera system controller 135 determines, via the operation detectingcircuit 136, whether or not the shooting/playback mode switch 127 isoperated. When the shooting/playback mode switch 127 is operated, stepS300 determines whether or not the current viewfinder mode is the OVFmode. When the OVF mode is set, the flow proceeds to the step S310; whenthe EVF mode is set, the flow proceeds to the step S301.

Step S310 controls driving of the information display circuit 142, anddeactivates the viewfinder field by the OVF information display unit180, thereby saving unnecessary power and battery consumptions.

Step S301 stores information on the viewfinder mode determined by thestep S300 in the memory 135 a in the camera system controller 135.

Step S302 reads the image data recorded in a recording medium (notshown) via a recording processor 133, and the playback processor 134processes the read image data. The display unit 107 displays the imagedata processed by the playback processor 134.

Step S303 invalidates or prohibits an input of the viewfinder modeswitch 123. This function prevents an unnecessary operation of theviewfinder mode switch 123, which would otherwise switch the viewfindermode in the playback mode. More specifically, when a playback mode isswitched to a shooting mode, this function prevents a switch of theviewfinder mode contrary to user's intent or to a mode different fromuser's memory.

Thereby, when the user selects the shooting mode after the display unit107 plays a captured image in response to a switch from the shootingmode to the playback mode, the user feels no discomfort with anobservation of the subject image. In the same viewfinder mode of theprevious shooting mode, the user can comfortably determine a scene forthe current shooting mode.

Step S304 waits for an input of a switch, such as a release button 129,while allowing the display unit 107 to display the captured image.

In step S305, the camera system controller 135 determines, via theoperation detecting circuit 136, whether or not any of various switches,such as the release button 120, are operated. When none of the switchesare operated, the flow proceeds to step S304. When the switch isoperated, the flow proceeds to step S306.

Step S306 determines whether the operated switch is theshooting/playback mode switch 127. When it is an input of theshooting/playback mode switch 127, the flow proceeds to step S307. Onthe other hand, when it is an input of another switch, such as an imagedeletion switch and a display screen switch (not shown), the flowproceeds to step S320.

Step S320 operates in accordance with the input of the other switch,such as a deletion of image data when it is an input of the imagedeletion switch, and a switch of a captured image on the display unit107 when it is an input of the display screen switch. The flow returnsto step S304 when the process in the step S320 ends, and waits for aninput.

Step S307 switches the playback mode to the shooting mode, and validatesthe input of the viewfinder mode switch 123, which is prohibited by thestep S303. Thereby, the user operates the viewfinder mode switch 123,and freely switches the viewfinder mode.

Step S308 determines whether or not the viewfinder mode stored in thestep S301 is the OVF mode. When it is the OVF mode, the flow proceeds tostep S330; when it is the EVF mode, the flow proceeds to step S309.

Step S330 activates the information display function in the viewfinderfield by the OVF information display unit 180 by controlling driving ofthe information display circuit 142. Since this embodiment invalidatesthe input of the viewfinder mode switch 123 in switching the shootingmode to the playback mode, the viewfinder mode does not switch and thehalf mirror 111 and the sub-mirror 122 are not driven. Therefore, whenthe OVF mode is set before the mode is switched to the playback mode,and then the playback mode is again switched to the shooting mode, theOVF mode is available only by driving the OVF information display unit180.

Step S309 provides a real-time display of the display unit 107. Asdiscussed above, when the shooting mode is switched to the playbackmode, the half mirror 111 and the sub-mirror 122 are not driven.Therefore, when the EVF mode is set before the mode is switched to theplayback mode, and then the playback mode is again switched to theshooting mode, the real-time display is available only by starting areadout of an image from the image-pickup device 106.

While this embodiment invalidates an operation of the viewfinder modeswitch 123 in the playback mode as discussed above, the presentinvention is not limited to this embodiment and the half mirror 111 andthe sub-mirror 122 may not be driven in the playback mode. For example,suppose that when another switch other than the viewfinder mode switch123 is operated, a switch of the viewfinder mode is adapted to associatewith an action in accordance with the command from the other switch.During the setting of the playback mode, the viewfinder mode can beadapted not to switch even when the other switch is operated.

A description will now be given of signal processing for a focusdetection by the focus detecting unit 121.

The (object) light emitted from the image-taking lens 103 a is reflectedon the half mirror 111 in the second optical path splitting state, andon the sub-mirror 122 on the first optical path splitting state, andthen enters the condenser lens 164 provided at the lower portion of themirror box. The light incident upon the condenser lens 164 deflects onthe mirror 165, and forms a secondary image of the object on the focusdetecting sensor 167 by an operation of a re-imaging lens 166.

The focus detecting sensor 167 has at least two pixel columns. Arelative lateral shift is seen between signal waveform outputs from thetwo pixel columns in accordance with the imaging state on the focusdetecting area of the object image that is formed by the image-takingoptical system 103. A shift direction of the output signal waveforminverts depending upon whether the imaging state is a front focus or aback focus. It is the principle of focus detection to detect a shiftdirection and a shift amount (or a phase difference) using such anapproach as the correlation operation.

FIGS. 11 and 12 show output signal waveforms of focus detecting sensor167 input to the AF controller 140. The abscissa axis indicates a pixelarrangement, and the ordinate axis indicates an output value of thefocus detecting sensor 167. FIG. 11 shows an output signal waveform at adefocus state from the object image. FIG. 12 shows an output signalwaveform at a focus state from the object image.

In general, the light used for focus detection is not the same as theimaging light in the aperture state but part of the imaging light. Inother words, the focus detection uses dark F-number light. When amechanical error in the camera is considered, a position of theimage-pickup device 106 and a position of the focus detecting sensor 167are not, strictly speaking, optically conjugate with each other.

Therefore, even in the focus state on the object image, as shown in FIG.12, there is a slight initial phase difference Δ between two outputsignal waveforms. This slight initial phase difference Δ is differentfrom that used for correction to a focus detection signal in the abovefocus correction mode (see step S206 in FIG. 8).

Since a true phase difference is given by subtracting the initial phasedifference Δ a phase difference detected through a correlation operationof two images, the initial phase difference Δ itself does not usuallypose a problem.

As described above, the sub-mirror 122 in the first optical pathsplitting state or the half mirror 111 in the second optical pathsplitting state can introduce the light used for the focus detection inthis embodiment. However, the reflection surface position of thesub-mirror 122 in the first optical path splitting state (FIG. 3) doesnot completely accord with the reflection surface position of the halfmirror 111 in the second optical path splitting state (FIG. 1) in viewof the mechanical accuracy, and different optical path splitting stateshave different values of the initial phase difference Δ. Thus, the truephase differences in the first and second optical path splitting statescannot be given merely by subtracting a constant initial phasedifference Δ from the phase difference detected through the correlationoperation.

The usual component processing accuracy may offset two reflectionpositions from each other by about 30 μm in the perpendicular directionof the reflection surface. An attempt to reduce the mechanical offset onthe reflection surface position would remarkably increase the componentprocessing cost.

Accordingly, this embodiment sets the initial phase differences Δ forthe first and second optical path splitting states, respectively, anduses the initial phase difference Δ corresponding to the selectedoptical path splitting state so as to correct the output signal of thefocus detecting sensor 167. Thereby, a true phase differencecorresponding to the selected optical path splitting state can beobtained, and precise focus detections are available based on the phasedifference.

Thus, whether or not the image-taking optical system is in the in-focusstate can be determined by determining the identity of a pair of signalsby considering the initial phase difference. The defocus amount can becalculated by detecting the phase difference using a known approach,such as an approach using the correlation operation disclosed, forexample, in Japanese Patent Publication No. 5-88445. The obtaineddefocus amount is converted into the driving amount of the focus lens103 b in the image-taking optical system 103, and the focus lens 103 bis driven by the driving amount for autofocus of the image-takingoptical system.

The phase difference detection uses a known driving amount of thefocusing lens 103 b, only one driving of the lens is usually enough toobtain the in-focus position, and can provide extremely high-speedfocusing.

This embodiment achieves the focus detection in the phase differencedetection by the focus detecting unit 121 in the EVF mode where thedisplay unit 107 displays the object image on the real-time basis, inaddition to the OVF mode where the viewfinder optical system is used toobserve the object image, accelerating the focusing of the image-takingoptical system. When the continuous shooting and motion-picture shootingare available in the second optical path splitting state (FIG. 1), theseshootings can obtain high-speed focusing. This embodiment does notrequire the conventional two focus detecting units, and prevents a largesize and increased cost of the camera system.

A prohibition of a switch of the viewfinder mode between the EVF modeand the OVF mode during driving of the focus lens 103 b prevents adefocus of the object image observed after the driving of the focus lensends.

An invalidation of any operations of the viewfinder mode switch 123during the playback mode does not cause a switch of the viewfinder modeset in a previous shooting mode to a different mode when the playbackmode is switched to another shooting mode. This non-switch of theviewfinder mode does not puzzle the user, and enables the user to set ascene in the same viewfinder mode as that set in the previous shootingmode to the playback mode.

While the above embodiment discusses the camera system that drives thehalf mirror and the sub-mirror independently, the present invention isapplicable to a camera system that drives the half mirror and thesub-mirror together. This embodiment arranges the half mirror and thesub-mirror on the shooting optical path in the OVF mode, retreats themfrom the shooting optical path in the EVF mode, and does not drive themin the playback mode.

This application claims foreign priority benefits based on JapanesePatent Applications Nos. 2004-108504 and 2004-108505, both filed on Mar.31, 2004, each of which is hereby incorporated by reference herein inits entirety as if fully set forth herein.

1. An image-taking apparatus comprising: an image-pickup device forphotoelectrically converting a subject image formed by light from animage-taking lens; a viewfinder optical system for enabling the subjectimage to be observed using the light; a focus detecting unit fordetecting focus of the image-taking lens using the light; a mirror unitswitchable between a first state and a second state to be switched, saidfirst state being used to introduce the light into said viewfinderoptical system and said focus detecting unit, and said second statebeing used to introduce the light to said image-pickup device and saidfocus detecting unit; and a controller for switching between said firststate of said mirror unit and said second state of said mirror unit, anddriving of a focus lens in the image-taking lens based on a detectionresult by said focus detecting unit, wherein a target driving positionof the focus lens differs between said first state of said mirror unitand said second state of said mirror unit, wherein said controllerprohibits the switching of said mirror unit while the focus lens isbeing driven.
 2. An image-taking apparatus according to claim 1, whereinsaid controller releases a prohibition of the switching of said mirrorunit in accordance with an input from the image-taking lens, of a signalindicative of a completion of driving of the focus lens.
 3. Animage-taking apparatus according to claim 1, further comprising anoperation member that is operated so as to command a switch between thefirst and second states, wherein said controller prohibits the switchingof said mirror unit corresponding to an operation of said operationmember while the focus lens is being driven in the image-taking lens. 4.An image-taking apparatus according to claim 1, wherein said first stateis used to reflect the light to said viewfinder optical system and saidfocus detecting unit, and wherein said second state is used to transmitthe light toward said image-pickup device, and to reflect the light tosaid focus detecting unit.
 5. An image-taking apparatus according toclaim 3, wherein said mirror unit includes: a first mirror member forreflecting part of the light and for transmitting the rest of the light;and a second mirror member for reflecting light that has transmittedthrough the first mirror member, wherein the first and second mirrormembers are arranged on an optical path of the light in the first state,wherein the first mirror member is located in the optical path and thesecond mirror member retreats from the optical path in the second state,and wherein the first and second members retreat from the optical pathat an image recording time.
 6. An image-taking system comprising: animage-taking apparatus according to claim 1; and an image-taking lens,attachable to said image-taking apparatus, for driving the focus lens inaccordance with control by the controller.
 7. An image-taking systemcomprising: an image-taking apparatus according to claim 2; and animage-taking lens, attachable to said image-taking apparatus, fordriving the focus lens in accordance with control by the controller, andfor outputting to said image-taking apparatus a signal indicative of acompletion of driving of the focus lens.
 8. An image-taking apparatuscomprising: an image-pickup device for photoelectrically converting asubject image formed by light from an image-taking lens; a viewfinderoptical system for enabling the subject image to be observed using thelight; a mirror unit switchable between a first state and a second stateto be switched, said first state being used to introduce the light tosaid viewfinder optical system and said focus detecting unit, and saidsecond state being used to introduce the light to said image-pickupdevice and said focus detecting unit; and a controller for switchingbetween said first state of said mirror unit and said second state ofsaid mirror unit, and for operating between a first mode used to recordan image using an output from said image-pickup device, and a secondmode used to display a playback image, wherein said controller prohibitsthe driving of said mirror unit while driving by said second mode.
 9. Animage-taking apparatus according to claim 8, further comprising anoperation member that is operated so as to command a switch between thefirst and second states, wherein said controller prohibits the drivingof said mirror unit corresponding to an operation of the operationmember in the second mode.
 10. An image-taking apparatus according toclaim 8, further comprising a focus detecting unit for detecting focusof the image-taking lens using the light, wherein the first state isused to reflect the light to said viewfinder optical system and saidfocus detecting unit, and wherein the second state is used to transmitthe light toward said image-pickup device and to reflect said focusdetecting unit.
 11. An image-taking apparatus according to claim 8,wherein said mirror unit includes: a first member for reflecting part ofthe light and for transmitting the rest of the light; and a secondmember for reflecting light that has transmitted through the firstmirror member; wherein the first and second mirror members are arrangedon an optical path of the light in the first state; wherein the firstmirror member is arranged on the optical path and the second memberretreats from the optical path in the second state; and wherein thefirst and second mirrors retreat the optical path at an image recordingtime.
 12. An image-taking system comprising: an image-taking apparatusaccording to claim 8; and an image-taking lens attachable to saidimage-taking apparatus.